1. Field of the Invention
This invention relates to an image recording apparatus for recording an image by emitting light beams to a recording material mounted on a recording drum.
2. Description of the Related Art
When printing in four color inks of yellow (Y), magenta (M), cyan (C) and black (K), for example, the same positional relationship must be maintained, for each of the YMCK colors, between a positioning bore for the printing machine used in positioning a printing plate, and an image recorded on the printing plate. The term “positioning bore for the printing machine” used in this specification includes a positioning bore used in placing the printing plate on a plate cylinder of the printing machine, and also a punch bore such as a positioning bore used in placing the printing plate on a puncher for forming a further punch bore in the printing plate.
In a method proposed in U.S. Pat. No. 6,213,020 (hereinafter called “the first method”), a positioning bore for positioning a recording material on a recording drum and a positioning bore for the printing machine are formed almost simultaneously in the recording material before attachment to the recording drum, and the recording material is positioned on the recording drum by using the former. Specifically, when attaching the recording material to the recording drum, the recording material is positioned relative to the recording drum by placing the positioning bore formed at an end of the recording material in contact with a positioning pin, and then the recording material is fixed to the recording drum.
In a method proposed in Japanese Unexamined Patent Publication No. 1997-152707 (hereinafter called “the second method”), a punch unit is disposed on a surface of a recording drum, and after attaching a recording material peripherally of the recording drum, the punch unit is used to form a positioning bore for the printing machine in the recording material for use in positioning a printing plate.
In the first method described above, the recording material is positioned on the recording drum by placing the positioning bore formed at an end of the recording material in contact with positioning pin. This method has a drawback that, where the recording material is a soft material, a deformation of the recording material makes it impossible to position the recording material accurately on the recording drum. This results in an inaccurate positional relationship between the positioning bore and a recorded image.
On the other hand, the second method described above requires the punch unit to be attached peripherally of the recording drum. When the recording drum is rotated at high speed, the weight of the punch unit will make it difficult to rotate the recording drum with high accuracy unless the weight balance of the entire recording drum is adjusted accurately. When the punch unit is customized, it is necessary to perform an adjustment of the weight balance of the recording drum again, and hence a drawback of the punch unit not being easy to customize.